While this is by no means a quantum leap for HIV treatment in humans, any AIDS progress is great AIDS progress. Especially when the progress is in our furry monkey relatives, who are responding terrifically to a new AIDS vaccine.

The vaccine, consisting of a genetically altered form of cytomegalovirus (CMV), prevented infection in 13 of the 24 rhesus macaques exposed to simian immunodeficiency virus (SIV), the monkey form of HIV. Now, monkey HIV isn't HIV—and monkeys aren't humans. But good news for our genetically-similar cousins could be good news for us—the authors of the study, published in Nature, say it could "significantly contribute" to a human vaccine.

So what's standing between us and them? Safety. "CMV is not totally benign, it does cause a number of diseases. If you're giving people something you're not going to be able to get rid of should it cause problems, then that's quite a difficult risk to manage," explains one researcher. "I'm scratching my head how to take this approach into humans."